Most importantly, how can I set realistic, effective metrics to guide my investment decisions?

You're realistically looking at 500k-1M of appreciation on $35k of invested cash.

You've shared so many gems and described a realistic depiction of purchasing an investment property. 

Big things is be realistic on timing and maybe provide a mover and or storage unit deposit as they may not be able to figure that part out on their own.

So let’s assume with realistic expense estimates over 1st 5 years you average $250 in today equivalent dollars (it will be a challenge at that starting point).The ADUs are typically receiving valuations below $100k, but let’s be generous to show the scope of the people and say it adds $150k of value. 

Although that is technically possible, it ain't that likely to happen....so be realistic.

if you do it right, you'll break even.not trying to be negative, just realistic.

Conducting inspections and due diligence on the condition of a property to derive realistic estimates for repairs is still the key.

This might be as simple as asking the sales Person how much money will I need to spend over the next 12 months on the business to have a realistic chance of succeeding at this.

I have an idea of an initial investment and returns I would like to hit, but would love to speak with those of actual experience to see if my numbers are realistic.